Under what condition should the engine be shut down immediately during ground operations?

The correct answer is that the engine should be shut down immediately during ground operations if the propeller safety zone is violated. This condition is critical for ensuring the safety of personnel on the ground and preventing potential accidents. The propeller safety zone is defined as the area around a running aircraft engine where the propeller can cause serious harm or injury due to its rapidly spinning blades. If anyone enters this zone while the engine is operational, they are at great risk, and immediate action must be taken to shut down the engine and mitigate that danger.

Other conditions, while they may warrant attention or caution, do not require an immediate shutdown of the engine as a safety protocol in the same manner. For example, exceeding an altitude of 200 feet during ground operations does not apply as ground operations typically refer to operations on the airport surface. Low fuel levels, although significant for flight operations, do not pose an immediate risk during ground operations apart from prompting pre-flight planning adjustments. Similarly, high exterior temperatures could affect engine performance or operational efficiency but do not necessitate an immediate shutdown for safety reasons like a violation of the propeller safety zone does.